Numerous varieties of plating technologies are known in the art. These technologies include electrolytic plating which is also known as electro-plating and by other terms, and electroless plating also known as chemical, autocatalytic and by other terms.
Electroless plating is a well known and established commercial/industrial process for metal plating. The metal portion of the metal salt may be selected from suitable metals capable of being deposited through electroless plating. Such metals include, without limitation, nickel, cobalt, copper, gold, palladium, iron, other transition metals, and mixtures thereof, and any of the metals deposited by the autocatalytic process described in Pearlstein, F., “Modern Electroplating”, Chapter 31, 3rd Ed., John Wiley & Sons, Inc. (1974), which is incorporated herein by reference. Generally, the electroless metal in the deposited coating is a metal, a metal alloy, a combination of metals, or a combination of metals and non-metals. Such coatings are often in the form of a metal, a metal and phosphorous, or a metal and boron. The metal or metal alloy is derived from the metal salt or metal salts used in the bath. Examples of the metal or metal alloy are nickel, nickel-phosphorous alloys, nickel-boron alloys, cobalt, cobalt-phosphorous alloys, and copper alloys. Other materials such as lead, cadmium, bismuth, antimony, thallium, copper, tin, and others can be deposited to form the bath and included in the coating.
The salt component of the metal salt may be any salt compound that aids and allows the dissolution of the metal portion in the bath solution. Such salts may include without limitation, sulfates, chlorides, acetates, phosphates, carbonates, and sulfamates, among others.
The reducing agents are electron donors. When reacted with the free floating metal ions in the bath solution, the electroless reducing agents reduce the metal ions, which are electron acceptors, to metal for deposition onto the article. The use of a reducing agent avoids the need to employ a current, as required in conventional electroplating. Common reducing agents are sodium hypophosphite, sodium borohydride, n-dimethylamine borane (DMAB), n-diethylamine borane (DEAB), formaldehyde, and hydrazine.
Certain materials may be used in electroless plating baths where these materials serve two or more roles in the plating bath. For example, instead of using the typical combination of nickel sulfate as a metal salt and sodium hypophosphite as a reducing agent, it is possible to use nickel-hypophosphite in an electroless nickel plating bath. Nickel-hypophosphite, however, is very expensive and not widely used commercially due to its impractical cost.
Electroless composite technology is a more recent development as compared to electrolytic composite technology. The fundamentals of composite electroless plating are documented in a text entitled “Electroless Plating Fundamentals and Applications,” edited by G. Mallory and J. B. Hajdu, Chapter 11, published by American Electroplaters and Surface Finishers Society (1990).